The Clinical Study Unit is a multicategorical research unit supported by the General Clinical Research Centers Branch of the National Institutes of Health. Progress reports of research projects were submitted with the annual report on February 1, 1973. We currently have 31 active in-patient protocols, 16 out-patient protocols. The number of out-patient protocols has increased significantly since the annual report for 1972 as received in 1973. The active in-patient protocols are these: 1) Radioimmuno Assay of Triiodothyronine(T-3, Its Significance in Passive Physiology in Thyroid Disease); 2) Renal Tubular Function in Renal Homograft Transplantation in Humans; 3) Series in the Physiochemical Characteristics of the Antiviral Antibody in Response to Immunization; 4) Clinical Study of Ureatherapy for Sickle-cell Vaso Occlusive Crisis; 5) Combination L- Asparaginase-Vincristine-Daunomycin Prednisone in Previously Treated Patients with Acute Leukemia; 6) Pharmacologic Studies of Anticonvulsants; 7) Further Evaluation of Phosphate in the Management of Hypercalcemia Diverse Etiologies; 8) Protocols for Diagnostic Studies and the Selection of Initial Treatment Programs in Patients with Malignant Lymphomas; 9) Studies of Potassium Supplments in Patients on Diuretics; 10) Study of Osteodystrophy and its Management; 11) Combined L-dopa and Alphamethyldopa or Alpha Methyldopahydrazine; 12) The role of Sodium Intake in Furosemide Administration in the Management of Hypertensive Azotemic Patients; 13) The Comparison of Intravenous Antihypertensive Agents Combined with Furosemide in Malignant Hypertension; 14) Trimterene and Spironolactone in Hypertensive Patients with High, Normal, and Supressed Renin Activity; 15) CP-18, 534-01 Hospitalized Patients; 16) The Application of the Metratonic CM Barostat CSNS for the Treatment fo Systemic Hypertension; 17) Gallium.